1. Field of the Invention
The invention relates to a monitoring device for a landfill or garbage dump in which a sealing liner is used. It also relates to a particularly favorable configuration of the sealing liner and to a process for localizing a leak in a sealing liner for a landfill. The invention does not only find application generally in the sealing and monitoring of waste dumps, but also in particular in the location of leaks in sites where hazardous industrial waste is deposited.
The Siemens prospectus "Long-term Dump Monitoring with LEOS", Order No. A 19100-U653-A222, July, 1991, discloses a device for sealing off a landfill and for detecting and locating leaks. In that case the landfill is provided with a water-tight liner, sealing web or "seal" (preferably made of synthetic material). The seal can be disposed underneath the body of the waste (base sealing), so that no pollutants can reach the groundwater. The seal can, however, also be laid above the body of the waste (surface sealing), in order to prevent ingress of rainwater and thus the washing out of pollutants from the waste. In order to detect a leak, i.e. a damaged location, in this seal early, in the case of the known device, provision is made for the laying of sensor hoses, that is to say of so-called LEOS hoses, specifically only on that side of the seal facing away from the body of the waste. In this case, LEOS stands for "leak location system".
The LEOS hoses, which are laid in a meandering or serpentine fashion, are filled with air and whose walls are permeable to various materials present in the dump, are connected to a central monitoring system. In the case of a placement of the seal underneath the body of the waste, a damage location therein is localized by detection of materials dissolved in the seepage water. And, in the case of a placement of the seal above the body of the waste, a damage location therein is localized by detecting rising foul gases.
An LEOS hose and a device used for its operation are disclosed in German patent DE-C 24 31 907. In this case a hose is utilized which is permeable to pollutants. At one end of the hose, a pump is disposed by which individual volumes of a transport medium, for example individual gas volumes, are successively fed at intervals in time through the hose. In this case, the hose is flowed through in each case for some time at uniform time intervals, i.e. at a constant frequency. At the other end of the hose there are sensors or detectors sensitive to the materials to be detected, particularly pollutants. In the event that a pollutant reaches the vicinity of the hose, this pollutant penetrates into the hose; it is taken to the sensors by means of the next pumping process of the transport medium. Since the medium in this case flows at a known speed, the location at which the pollutant has entered into the hose between two through-flow processes can be determined exactly from the difference between the switch-on instant of the pump and the response instant of the sensors. In addition, the quantity of pollutant can be determined.
German Utility Model G 91 07 693.5 and U.S. Pat. No. 5,215,409 describe a device for sealing and monitoring a body, preferably a waste dump, by means of a monitoring space. That disclosure is based on the knowledge that it is sensible to provide increased protection by means of a double barrier. This is expedient both in sealing the base and sealing the surface of a dump. Furthermore, the element is based on the consideration that it is also sensible to construct the system in such a way that it can be determined by measurement whether one or the other barrier has a leak and where the leak is. For this purpose, the element comprises two seals or sealing liners, which are spaced from each other by means of support elements. In so doing, at least one channel is formed between the seals and the supporting elements, which has an entry opening and an exit opening for a transport medium, such as for example air. This channel, in this case, is designed as a permeable LEOS hose, or it contains such a LEOS hose. At least one sensor, for example a sensor for liquid vapor and a sensor for gas, can be connected to the outlet opening. The two seals are connected to each other in a sealing manner at their edges, leaving free the inlet and outlet openings of the channel, so that the monitoring space is formed. The supporting elements comprise a material which is flow-permeable but flow-restricting (largely homogeneous). The hose can be surrounded by a filling material which holds back moisture, i.e. a drying medium.
Therefore, in the case of the last-named monitoring device, a monitoring space is an essential component, in which monitoring channels (permeable to the pollutant to be detected) or sensor hoses are incorporated, whose content is washed at regular time intervals in the direction of the detector. The monitoring space comprises walls closed on all sides, which are formed preferably from polyethylene webs or polyethylene liners. The space is vacuum-tight.
It now transpires that such a monitoring space in synthetic material technology can also be used on steep or even vertical wall regions of a landfill only at great cost. As an example, there are such vertical wall regions in special industrial landfills which are constructed using concrete troughs. As a result of thermal stresses of the concrete during hardening, under certain circumstances there are shrinkage cracks in the concrete, which can lead, in turn, to breaks in the adjacent polyethylene web and thus to a collapse of the double seal. Furthermore, it has transpired that the preparation of double-seal webs can be very expensive. A solution would thus be desireable which manages at a comparably lower cost.